The telecommunication operators focus on the Inter-net of Things (IoT) and route the traffic of several clients on a multi-hop infrastructure. Operators need to offer Service Level Agreements (SLAs) to each client, guaranteeing a minimum reliability or a maximum delay for each application. The deterministic IETF 6TiSCH protocol stack is particularly appropriate to provide SLA guarantees, because it allocates dedicated time-frequency blocks for a given traffic. We propose Kausa, a scheduling algorithm to assign a route and allocate resources to each client flow. We optimize the network lifetime while respecting the flow-level requirements. Kausa efficiently deals with lossy links, by scheduling ad-hoc retransmission opportunities. It limits both the buffer occupation and the end-to-end delay. Our simulations mimic multiple scenarios on multi-hop topologies, highlighting the relevance of our approach.